1. Field of the Invention
The present invention relates to a power supply apparatus. More particularly, the present invention relates to a power supply apparatus which supplies power to a controller using main and sub batteries as a power source.
2. Description of the Related Art
A controller is an element which drives and controls electrical parts according to user instructions, and is often considered to be the most essential part of an electronic device. Even when the electronic device is not in operation, that is, even in a power-off state, the controller sometimes remains operating. For example, the controller may be on to drive a timer to keep user-set time during the power-off of the electronic device.
Accordingly, power supply must continue to supply power even in the power-off of the electronic device. Meanwhile, in a general electronic device, there are two batteries used as a power supply for the electronic device and the controller. In the normal operation, the main battery is used to supply power to the controller. However, in the absence of main battery or main battery discharge, a sub battery is used to supply power to the controller.
FIG. 1 is a circuit diagram of a conventional apparatus for supplying power to the controller. Referring to FIG. 1, the power supply apparatus includes a main battery 10, a sub battery 20 and a diode 30 as a switching element.
In the presence of the main battery 10, power of the main battery 10 is supplied to the controller, while the power of the sub battery 20 is blocked by the diode 30.
In the absence of the main battery 10 or in case of main battery discharge, power is supplied from the sub battery 30 to the controller through the diode 30.
Because only the diode 30 operates to switch supply power supply to the controller, the power supply switching was not stable enough in the conventional power supply apparatus.
Additionally, when the sub battery 20 is insufficiently charged, that is, when the electrical potential of the sub battery 20 is lower than the potential barrier of the diode 30, power of the main battery 10 is supplied to the controller even when the main battery 10 is discharged. As the discharged battery is used, the lifespan of the battery 10 shortens.
Accordingly, a more stable power switching method of the main and sub batteries 10 and 20 is required, and also, a method to prevent use of main battery 10 in the case of discharge is also required.
Additionally, a method of using a controller power supply apparatus to stabilize reset of the controller, is also required.